mk/spdk: increase debugging info level to -g3

Default level is -g2, increasing it allows for
macro expansion at least for gcc.

Please try one of the below in gdb:
macro expand SPDK_MACRO(args)
print SPDK_VALUE

Signed-off-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Change-Id: Iaf9cfe54db9c97c804ea62be18fe5f0fa288ac77
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/19451


Reviewed-by: Aleksey Marchuk <alexeymar@nvidia.com>
Community-CI: Mellanox Build Bot
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>